Sand has long been used in foundry operations in making cores. The cores are employed in a casting process to ultimately provide voids in the casting. The cores are shaped so as to provide a void of a desired size and shape and to serve this purpose, it is necessary that the cores retain their integrity through the casting process until the molten metal employed in the casting process has solidified. When that occurs, the core is then broken up typically in a so-called "shake out" process, leaving a void of the desired size and shape within the casting.
To assure that the sand cores retain their desired size and shape during the casting process and yet can be broken up relatively easily to separate from the casting resulting from the process, it has been conventional to employ various organic resins as a binder to bind the grains of sand together to provide the structural integrity required. Although the amount of binder employed may vary depending upon the type of resin used, it is fairly typical to employ a resin content of about 2%, particularly in the so-called phenolic ester nobake process. Other foundry binder system include phenolic urethane coldbox, furan nobake, phenolic urethane nobake, and phenolic hotbox.
While these resins work well for their intended purpose, at the conclusion of the casting process, following shake out, a resin residue remains on the grains of sand and/or the sand may be in clumps, still held together by the binder. Whereas in the past, such sand was simply disposed of, environmental concerns have strongly suggested that the sand be reused wherever possible. Unfortunately, the presence of spent resin binder on the sand makes it impossible to use the same effectively and efficiently without first removing the resin residue.
To accomplish reclamation of the sand, one system proposed includes an indirectly heated rotary kiln, a rotary sand cooler, a pneumatic scrubber and classifier, a second rotary kiln, a second rotary sand cooler, and a second pneumatic scrubber and classifier. Shake out sand and other sand containing resin that results from the foundry operation, including the formation of the cores, is first reduced to small clumps or individual particles using a vibratory crusher. The sand may then be run through a magnetic separator to remove so called "tramp" metal and then is transported to the first kiln. The kiln is basically a drum including internal lifter bars which run lengthwise and lift the sand and carry it from the bottom of the drum to near the top where the sand then falls off of the lifter bar and tumbles through the interior of the drum which is provided with hot air from a heater. The hot air may be 1,250.degree. F. or more and as a consequence, the oxygen in the air and the heat act to combust the resin on the sand. Such residue as remains is dried and embrittled so that it can be scrubbed from the sand grains in the first scrubber/classifier. This process is essentially repeated in the second set of kiln, cooler and scrubber/classifier and the result is sand that has been reclaimed to the quality needed for reuse in resin binder systems.
While the system is operative to achieve its intended purpose, it is unnecessarily complex, and therefore, expensive. Furthermore, because heat transfer to the sand is achieved basically only by the heated air and/or contact of the sand grains with a heated drum, it is relatively slow and residence time is undesirably long. This in turn results in relatively large equipment in order to process a given quantity of sand to be reclaimed over a given time period. And, of course, the large equipment necessitates an undesirably large amount of floor space to house the same.
The present invention is directed to overcoming one or more of the above problems.